Production of electrolytic nickel



1. L. s. RENZONI ET AL 3,437,571

PRODUCTION OF ELECTROLYTIC NICKEL April 8,

Sheet Filed July 20. 1964:

INVENTORS LOUIS S. GEORGE A.

RENZONI DI BAR! BURTON B. KNAPP RANCIS X. CARLIN I. ATTORNEY April 8, 1969 L. s. RENZONI ET AL 3,437,571

PRODUCTION OF ELECTROLYTIC NICKEL Sheet ,2 of2 Filed July 20, 1964 INVENTORS IIPN NRP OAAL ZBNR Y N K A E E C RD N B I. x AN wm OS wm T I c URUN A OOBA LE R G F 3,437,571 PRODUCTIQN F ELECTROLYTIC NICKEL Louis S. Renzoni, Toronto, Ontario, Canada, George Angelo Di Bari, Haverstraw, N.Y., and Burton B. Knapp, Westfield, and Francis X. Carlin, Elizabeth, N.J., assignors to The International Nickel Company, Inc.,

New York, N.Y., a corporation of Delaware Filed July 20, 1964, Ser. No. 383,888

Int. Cl. C2211 1/14 U.S. Cl. 204-412 4 Claims ABSTRACT OF THE DISCLOSURE Electrolytic nickel having good appearance and good shearability in heavy sections and good chemical and electrochemical activity is produced by an electrorefining process wherein about 0.005 to about 0.25 gram per liter of sulfur dioxide and about 25 to about 75 milligrams per liter of a sulfur-free agent such as hydracrylonitrile are maintained in the electrorefining catholyte.

The present invention is directed to the electrorefining of nickel and, more particularly, to an improved method for producing electrolytic nickel or cathode nickel having good surface quality and having improved chemical and electrochemical activity.

The method for electrorefining nickel using impure nickel metal anodes is described in the Renzoni US. Patent No. 2,394,874 and the method for electrorefining nickel using nickel matte anodes is described in the Renzoni et al. US. Patent No. 2,839,461. In the method described in each of these patents, the electrorefining cell employed is a compartmented cell divided into anode and cathode compartments by means of a permeable diaphragm and the electrolyte employed is a sulfate-chloride electrolyte. The impure anode in the anode compartment is electrolytically corroded and substantially pure cathode nickel is deposited at a cathode in the cathode compartment as a result of electrolysis. The impure anolyte is removed from the anode compartment at a steady rate and is subjected to purification treatments to remove therefrom impurities such as iron, copper, lead, arsenic, etc. The purified electrolyte is then introduced at a steady rate into the cathode compartment and nickel of high purity is plated therefrom. A slight hydrostatic head is maintained in the cathode compartment, allowing purified catholyte partly depleted in nickel to flow through the diaphragm into the anode compartment, thus preventing migration of unwanted ions from the impure anolyte in the anode compartment to the purified catholyte in the cathode compartment. As the process proceeds, nickel and impurities are dissolved from the anode. The impure anolyte is removed from the tanks, purified, and finally returned as purified catholyte to each cathode compartment for the deposition of pure nickel at each cathode.

The production of cathode nickel is carried out commercially on a very large scale. For example, in one Canadian electrorefining installation the circulating rate of the electrolyte is approximately 300,000 gallons per hour. Because of the scale at which the operation is conducted and because of the necessity for producing electrolytic nickel under continuous conditions to produce a marketable product of high purity and having acceptable surface appearance, extremely careful control is required in all phases of the operation to insure that continuous production of cathodes can be maintained.

It has been recognized heretofore that there are industrial applications for which it is desirable to provide electrolytic nickel or cathode nickel having improved chemical and electrochemical activity. Reference may be made 3,437,571 Patented Apr. 8, 1969 in this connection to the Renzoni U.S. Patents Nos. 2,453,757 and 2,623,848. It has also been recognized heretofore that it is desirable to produce thick cathode nickel which would, nevertheless, have acceptable surface smoothness, freedom from nodularity, and good appearance. Reference may be made in this connection to the Brandt U.S. Patent No. 3,114,687. It has been found in practice that the cathode nickel having improved chemical and electrochemical activity produced by prior processes suffered disadvantages from the commercial viewpoint. Thus, it was difiicult under prior practices to produce cathode nickel having improved chemical and electrochemical activity but which would, nevertheless, have satisfactory ductility, shearability, good surface appearance, and high purity.

It has now been discovered that electrolytic nickel or cathode nickel having acceptable ductility, surface appearance and activity can be produced in an electrorefining operation by the addition of controlled amounts of a special combination of ingredients to the purified electrolyte.

It is an object of the present invention to provide a process for producing cathode nickel having improved chemical and electrochemical activity.

Another object of the invention is to provide a special method for producing cathode nickel having improved activity and also having satisfactory surface appearance and ductility.

Still another object of the invention is to provide a method for producing cathode nickel having improved activity at an acceptable purity level.

A further object of the invention is to provide a method for producing smooth cathode nickel with minimum disruption of the electrorefining operation.

Other objects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawing in which:

FIGURES 1 and 2 are reproductions of photographs taken at about 1 /2 diameters showing sheared pieces of electrolytic nickel produced outside the contemplation of the present invention;

FIGURE 3 is a reproduction of a photograph taken at about 1 /2 diameters showing two sheared pieces of the activated shearable electrolytic nickel produced in accordance with the present invention; and

FIGURE 4 is a reproduction of a photomicrograph taken at about 50 diameter depicting certain characterizing features found in the structure of the specialactivated electrolytic nickel produced in accordance with the teachings of the present invention.

Generally speaking, the present invention contemplates a process for the production of electrolytic nickel cathodes which comprises electrolyzing an aqueous nickel electrorefining catholyte essentially devoid of impurities from the group consisting of copper, iron, arsenic and lead and containing a small amount, e.g., about 0.005 gram per liter, up to about 0.025 gram per liter of sulfur dioxide and a small amount, e.g., about 25 milligrams per liter up to not more than about milligrams per liter, of a sulfur-free leveling agent dissolved therein to produce sound, electrolytic nickel containing about 0.005% to about 0.025% sulfur substantially uniformly distributed therethrough. More advantageously, the electrolyte contains about 0.01 to about 0.02 gram per liter of sulfur dioxide and the cathode nickel produced contains about 0.01% to about 0.02% sulfur. The electrolysis is carried out while maintaining the electrolyte temperature between about F. and F. and while employing a cathode current density between about 5 and 25 amperes per square foot.

The electrorefining electrolyte may be the all-sulfate type, the all-chloride type, the all-sulfamate type, or may contain mixtures of these three salts. At the present time, the sulfate-chloride electrolyte is generally employed. It is to be appreciated that the process is applicable not only to the production of commercial electrolytic nickel conventionally having a thickness on the order of about inch to about /2 inch but it also is applicable to the production of the thin nickel cathode starting sheets employed in producing commercial cathode nickel. Such starting sheets are usually about 0.04 inch thick. Advantageously, the leveling agent employed in accordance with the invention is a water-soluble organic cyanide or nitrile, i.e., a compound containing the CEN group attached to a carbon atom. More advantageously, such agents are employed in the ranges of about 30 to about 40 milligrams per liter of purified electrolyte. Examples of such compounds are ethylene cyanohydrin (hydracrylonitrile) (CI-I II-ICH -CN), acetonitrile (CH ,CN), acrylonitrile (CH zCH CN), acetaldehyde cyanohydrin (CH CHOI-ICN) cyanoacetic acid acetone cyanohydrin (CH -COH-CN) propionitrile (CH CH -CN) 2-cyanoacetamide beta-chloropropionitrile (ClCH -CH CN), benzonitrile (C H CN), and para amino phenyl acetonitrile (NH C H CH -CN). Such organic cyanides may be saturated or unsaturated, aliphatic or aromatic and may also contain a substituted group such as halogen, hydroxy, amino or carboxy group. Another sulfur-free agent which may be employed along with or in place of organic cyanides is coumarin.

It has been found that the special process defined hereinbefore provides the unexpected and unobvious result that sulfur introduced into the cathode nickel is substantially uniformly distributed therethrough. This highly advantageous effect is believed to contribute importantly to the appearance of the product and yields a cathode nickel product having improved chemical and electrochemical activity at a very low sulfur level, e.g., 0.02% sulfur. Thus, it was known from prior work involving the use of sulfur dioxide as the sole sulfur-containing additive to the electrorefining bath that in order to produce a cathode nickel which would have electrochemical activity of such a nature that it could be used directly to supply nickel ions to solution when subjected to electrochemical corrosion in a conventional nickel plating bath such as the Wattstype bath that the sulfur content should be in excess of about 0.03%, e.g., about 0.06% or more. The electrolytic nickel thus produced was dark in color and also tended to be quite nodular and brittle. The poor appearance and shearing difficulties encountered with this product rendered it unsatisfactory from a commercial viewpoint. It had further been observed from prior work that cathode nickel containing sulfur at the level of about 0.02% as a result of electrorefining wherein sulfur dioxide was the sole sulfur-containing agent added to the electrolyte was quite inactive electrochemically and did not corrode smoothly, but rather became spongy, when subjected to electrochemical corrosion as, for example, in a conventional nickel plating bath. It had been found that an eX- pensive heat treatment at a high temperature on the order of 1500 F. to about 1800 F. Was required in order to achieve an acceptable level of electrochemical activity in this prior cathode nickel product. It is believed that these prior observations resulted from and were due to a nonuniform or segregated occurrence of sulfur in the cathode nickel product.

The electrolytic nickel cathode produced in accordance with the present invention contains sulfur distributed therethrough in an essentially uniform manner and no heat treatment is required in order to provide a satisfactory level of electrochemical activity in the cathode nickel product even though the sulfur level is very low, e.g., about 0.02%. Thus, active cathode nickel produced in accordance with the invention exhibits a negative potential on the order of about minus 0.1 volt as measured against a standard calomel electrode (S.C.E.) up to an anodic current density of about 150 amperes per square foot in an aqueous electrolyte containing about 70 grams per liter of nickel, about grams per liter of sulfate ion, about 30 grams per liter of boric acid, having a pH of about 4 and at a temperature of F. In this electrolyte, commercial electrolytic nickel becomes passive at about one ampere per square foot. In addition, cathode nickel produced in accordance with the invention has a commercially acceptable, attractive appearance, is readily shearable to give a smooth shear cut, and corrodes smoothly when subjected to electrochemical corrosion as, for example, in a conventional nickel plating bath.

Comparison of the electrolytic nickel pieces depicted in FIGURES 1 and 2 with the electrolytic nickel pieces depicted in FIGURE 3 demonstrates that the nickel produced in accordance with the present invention (FIG- URE 3) is very substantially improved in appearance and shear-ability. All the nickel depicted was produced in a similar fashion but the nickel depicted in FIGURES 1 and 2 contained sulfur at the level of about 0.05%. This material was quite dark in color, was undesirably brittle, as is indicated by the cracking behind the shear cuts, and did not shear to give a smooth shear cut. The commercial acceptability of this material is poor. In contrast thereto, the nickel depicted in FIGURE 3, at a sulfur level of about 0.02%, is bright and attractive in appearance and shears readily to provide a smooth, clean, shear cut. This mate rial finds ready commercial acceptance on the basis of appearance and its special properties, including the fact that when it is corroded electrochemically in conventional nickel plating baths the corrosion is smooth and uniform and there is essentially no loose nickel with very little sludge resulting from the corrosion.

It has been found that the special electrolytic nickel produced in accordance with the invention has an unusual microstructure, including as characterizing features areas of an apparent dendritic structure presenting a pine tree effect and quite pronounced striae or hands or laminae of a darker-etching appearance. The said bands or striae evidently are islands which appear randomly in the structure. FIGURE 4 in the drawing depicts areas of the darker etching striae and areas of pine tree" effect. The grain size of the special electrolytic nickel is fine.

For the purpose of giving those skilled in the art a better understanding of the invention, the following illustrative example is given:

EXAMPLE To a portion of a purified electrolyte having a pH of about 4.0 and containing about 55 grams per liter of nickel, about 20 grams per liter of sodium, about 46 grams per liter of chloride ion, about 87 grams per liter of sulfate ion, about 18 grams per liter of boric acid, about 0.3 gram per liter of calcium ion, and less than about 0.004 gram per liter total of copper, lead, arsenic and iron, about 0.02 gram per liter of sulfur dioxide, and about 0.04 gram per liter of ethylene cyanohydrin were added. A thin nickel starting sheet was immersed in the electrolyte and current was passed through the electrolyte at a cathode current density of 15 amperes per square foot with the electrolyte temperature being about 140 F. Nickel from the electrolyte was deposited upon both faces of the nickel starting sheet in order to grow a cathode having a total thickness of /2 inch. The resulting cathode contained about 0.02% sulfur and was found to have a bright, smooth appearance. The cathode was sheared into pieces about one inch square and it was found that the material sheared readily to give a smooth cut face. Portions thereof were inserted in a titanium plating basket immersed in a standard Watts-type bath.

The cathode nickel material corroded smoothly with essentially no production of metallic nickel and with only a minor proportion of sludge being formed during the corrosion. The cathode material exhibited a negative potential of about 0.1 volt when measured against S.C.E. in an all-sulfate bath. In addition, the material exhibited high chemical activity in that about 43% of a test coupon made therefrom dissolved in five hours exposure without agitation to an aqueous solution (1 :1 ratio) of nitric acid (70.2% HNO by weight) whereas under similar conditions only 17% of a similar test coupon made of conventional electrolytic nickel was dissolved.

Satisfactory aqueous electrolytes which may be employed in the electrorefining operation in accordance with the present invention have compositions as set forth in the following table.

Range, grams Composition: per liter Sulfate-chloride electrolytes Nickel 40-70 Sodium 20-30 Chloride 40-60 Sulfate 50-100 Boric acid -25 pH 3-5 All-sulfate electrolytes Nickel 40-70 Sodium 4-8 Sulfate 75-130 Boric acid 10-40 pH 3-5 All-chloride electrolytes Nickel 40-70 Chloride 55-85 Boric acid 10-40 pH 4-5 All-sulfamate electrolytes Nickel 60-130 Sulfamate 175-350 Boric acid 10-40 pH 3.8-4.5

In accordance with the concepts of the present invention, sulfur dioxide is the advantageous ingredient employed in the electrolyte for the purpose of introducing sulfur into the special cathode nickel provided in accordance with the invention. Thus, the sulfur dioxide content of the electrolyte can be removed completely merely by aerating the electrolyte which may thereupon be employed for the purpose of producing electrolytic nickel essentially devoid of sulfur. It is also to be appreciated that the sulfur content of the special cathode nickel produced produced in accordance with the invention can be replaced wholly or partly by at least one element from the group consisting of selenium, tellurium and phosphorus. When such agents are employed they may be introduced into the electrolyte in the form of compounds which do not contain metallic cations. Thus, selenium may, advantageously, be introduced into the electrolyte in the form of selenous acid in the amount of about 0.007 to about 0.08 gram per liter to introduce about 0.01% to about 0.2% of selenium into the cathode nickel. Tellurium may be introduced into the electrolyte in the form of tellurium dioxide in the amount of 0.005 to 0.06 gram per liter to introduce about 0.01% to about 0.1% of tellurium into the cathode nickel and phosphorus may be introduced into the electrolyte in the form of hypophosphorus acid in the amount of about 0.01 to about 1.5 grams per liter to introduce about 0.02% to about 3% of phosphorus into the cathode nickel. When such materials are employed, it is still advantageous also to employ at least about 0.01 gram per liter of sulfur dioxide in the electrolyte to produce cathode nickel containing about 0.01% of sulfur along with the other substituent. Cathode nickel having increased chemical and electrochemical activity is useful in many industrial applications, including electroplating, the production of nickel salts, etc.

While the exact theoretical explanation of the technical phenomena underlying the present invention is not fully understood, it appears that the production of electrolytic nickel having in the as-deposited condition improved electrochemical activity and corrodability along with a highly satisfactory appearance and good shearing characteristics in a commercial scale refinery under controllable conditions is achieved by incorporating in the electrolyte a special combination of special amounts of ingredients, including sulfur dioxide and an agent such as hydracrylonitrile. It is recognized generally that the structure of electrodeposited metals is unique due to the conditions under which the deposit is formed. Thus, electrolytically deposited metals can offer a variety of structures. Such metals usually are stressed, have dislocations in the structure and, at times, may demonstrate crystalline formations which are similar to dendrites formed from molten metals. The complexity of the problem of producing metals on a large scale in a commercial electrolytic refinery is so great that the problem of producing such metals, e.g., nickel, having controlled properties in the as-deposited condition is one of great difiiculty. It appears that in accordance with the present invention, the deposition of sulfur from sulfur dioxide in the electrolyte has been effected in a particularly advantageous manner with the result that a highly satisfactory commercial product having an enhanced combination of chemical and physical properties in the asdeposited condition may now be produced on a very large commercial scale and with a minimum of interference with refinery operations. All indications which have been obtained in practice with the commercial product produced in accordance with the invention point to an essentially uniform distribution of sulfur therein. This factor makes it particularly difiicult to explain satisfactorily the variety of microstuctures which have been observed in the product. Nevertheless, it appears that the darker bandings or striations which occur in the structure of the product are characteristic. It may be noted in this connection that commercial electrolytic nickel devoid of sulfur displays an essentially uniform microstructure.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such variations and modifications are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. In the process for electrorefining impure nickel material, the improvement for producing electrolytic nickel having a high combination of chemical and physical properties, including electrochemical activity, shearability, and good surface appearance, which comprises establishing an aqueous acid nickel electrorefining electrolyte having dissolved therein about 0.01 to about 0.02 gram per liter of sulfur dioxide and about 25 to about 75 milligrams per liter of hydracrylonitrile, immersing a cathode therein, and passing current at a cathode current density of about 5 to about 25 amperes per square foot through said electrolyte to said cathode while maintaining the temperature of said electrolyte between about F. and about F. to deposit electrolytic nickel containing sulfur in a controlled amount of about 0.01% to about 0.02% distributed therethrough.

2. The process according to claim 1 wherein the dissolved hydracrylonitrile is between about 30 and about 40 milligrams per liter.

3. In the process for electrorefining impure nickel material, the improvement for producing electrolytic nickel having a high combination of chemical and physical properties, including electrochemical activity, shearability, and good surface appearance, which comprises establishing an aqueous acid electrorefining electrolyte having dissolved therein at least one agent from the group consisting of about 0.005 to about 0.025 gram per liter of sulfur dioxide, about 0.007 to about 0.08 gram per liter of selenous acid, about 0.005 to about 0.06 gram per liter of tellurium dioxide, and about 0.01 to about 1.5 grams per liter of hypophosphorous acid, and about 25 to about 75 mill-igrams per liter of at least one agent from the group consisting of hydracrylonitrile, acetonitrile, acrylonitrile, acetaldehyde cyanohydrin, cyanoacetic acid, acetone cyanohydrin, propionitrile, Z-cyanoacetarnide, beta-chloropropionitrile, benzonitrile, para amino phenyl acetonitrile, and coumarin, passing current through said electrolyte at a cathode current density of about to about 25 amperes per square foot, While maintaining the electrolyte temperature at about 100 F. to about 160 F., to produce electrolytic cathode nickel containing at least one agent from the group consisting of about 0.005% to about 0.025% sulfur, about 0.01% to about 0.2% selenium, about 0.01% to about 0.1% tellurium, and about 0.02% to about 3% phosphorus distributed therethrough.

4. As a new article of manufacture, electrolytic nickel containing about 0.01% to about 0.02% sulfur distributed therethrough and characterized in the as-deposited condition by high electrochemical activity, including a negative potential on the order of about minus 0.1 volt as measured against a standard calomel electrode up to an anod-ic current density of about 150 amperes per square foot in an aqueous electrolyte consisting essentially of about grams per liter of nickel sulfate, about grams per liter of sulfate ion, a pH of about 4- and a temperature of about F., by good surface appearance and shearability in sections at least three-eighths inch thick, and the ability to corrode smoothly when subjected to electrochemical corrosion and by a microstructure including readily-etched, fine-grained striations.

References Cited UNITED STATES PATENTS 2,125,229 7/1938 Harshaw et al. 204-49 2,392,708 1/ 1946 Tschop 204-49 2,524,010 9/1950 Du Rose et al 204-49 2,623,848 12/1952 Renzo'ni 204-112 2,635,076 4/1953 Du Rose 204-49 3,090,733 5/1963 Brown 204-49 3,114,687 12/1963 Brandt 204-49 FOREIGN PATENTS 525,848 9/1940 Great Britain.

JOHN H. MACK, Primary Examiner.

H. M. FLOURNOY, Assistant Examiner. 

